Ischemic heart disease caused by atherosclerosis is the leading cause of morbidity and mortality among U.S. Veterans. Atherosclerosis is a chronic inflammatory disease characterized by heterogeneous, lipid-laden vascular plaques. Inflammatory plaques have traditionally been at high risk of rupture leading to clot formation and subsequent heart attack. Identifying calcified plaque has a predictive value in terms of overall atherosclerotic burden; however, inflammatory high-risk plaques tend to have minimal or spotty levels of calcium deposition. Thus some plaques are minimally calcified and very inflammatory in nature, whereas other types of plaque are heavily calcified and appear less inflammatory and less likely to rupture. Little is known about what mechanisms drive the evolution of plaque calcium composition. Macrophage adhesion signaling is critical to the augmentation pro-inflammatory factors secreted by macrophages, including proteases that remodel extracellular matrix. Cytoskeletal elements like Rac2 and Myosin IIA appear to be critical modulators of that adhesion-based inflammatory signaling and thus would make excellent potential targets for inhibiting plaque inflammation and reducing the risk of heart attack. Preliminary data in a Rac2 gene-deletion, atherosclerosis-prone mouse model demonstrates the evolution of heavily calcified plaques that are likely to be less inflammatory. The goal of this study is to define the mechanisms that drive this heavy calcification and to quantify whether heavy calcification truly represents decreased inflammatory activity within the plaque. Plaque calcium composition is thought to be derived from a balance between anabolic (calcium-promoting) osteoblasts and catabolic (calcium and matrix remodeling) osteoclasts. Macrophage subsets have the capacity to become osteoclast-like cells. Thus, the primary hypothesis is that adhesion signaling in macrophages, through Rac2- Myosin IIA networks, is a critical modulator of macrophage-derived osteoclast-like cell, leading to their effective differentiation and effector function, which serves to minimize calcific depositon in plaques and maintain an inflammatory phenotype. This hypothesis leads to three primary objectives that form the experimental design. The first objective is to define the dependence of osteoclast-like cell differentiation and function on Rac2 and Myosin IIA, using markers of osteoclast differentiation and the mineralized calcium resorption for function assessment. The second objective is to identify inflammatory factors, like matrix remodeling proteins, whose expression is driven by Rac2 and Myosin IIA through osteoclast-like cell adhesion, using molecular and biochemical techniques. The third and final aim is to define the dependence of calcific atherosclerosis on Myosin IIA and to quantify an inverse correlation between the degree of calcification and the expression of inflammatory markers in vivo, using molecular imaging tools and the atherosclerosis-prone animal model. Defining the inflammatory mechanisms that modulate calcification of atherosclerotic plaques will lead to identification of novel therapeutic targets for the development of new medications that can reduce the risk of heart attack, ultimately having a profound effect on the lives of U.S. Veterans.